An epoxy compound is being widely utilized as an epoxy monomer working out to a raw material of an epoxy resin or as a raw material of various chemical products.
The epoxy resin is a resin obtained by curing an epoxy monomer by using various curing agents. The epoxy resin is a resin excellent in the mechanical property, water resistance, chemical resistance, heat resistance, electric property and the like and is used in a wide range of fields such as electronic material, optical material, building material, adhesive, coating material, laminated plate, molding material, casting material and resist.
Recently, the increased integration in the electronic material field, for example, fields of semiconductor sealing material, printed wiring board, build-up wiring board and solder resist, accompanies requirement to highly purify also a package material typified by an epoxy resin. Furthermore, in the optoelectronics-related field, highly advanced informatization in recent years leads to the development of a technique utilizing optical signals so as to smoothly transmit and process vast amounts of information and amid this trend, development of a high-purity resin excellent in the transparency is demanded.
With such growing needs for a high-purity epoxy resin, high purification is required also of the epoxy monomer working out to a material of the epoxy resin.
A glycidyl ether compound as a representative epoxy monomer, for example, a compound obtained by fusing a glycidyl oxy group to phenols, naphthols, bisphenol A, etc., is excellent in the heat resistance, adhesiveness, chemical resistance, electric properties, mechanical properties and the like and therefore, is an industrial material finding many applications such as adhesive, molding material, sealing material and coating material when crosslinked/cured by a curing agent. As the production method of the glycidyl ether compound, in the case of using phenols as the raw material, a method of reacting epichlorohydrin with the raw material phenols is most widely employed. A specific method for synthesizing a glycidyl ether by using epichlorohydrin is represented, for example, by the following reaction formula:

However, in the epoxy compound obtained by the above-described method, a chlorine atom derived from epichlorohydrin is mixed as an impurity in the form of being chemically bonded to the compound. Therefore, the chlorine concentration in the epoxy compound is high. Specifically, chlorine is usually contained at a concentration of 1,000 ppm or more. When an epoxy resin produced from an epoxy compound (epoxy monomer) having such a high chlorine concentration is used for an IC sealing material, there is a problem that corrosion or breakage of wiring is likely to occur due to refinement of the circuit for high integration.
To avoid such a problem, an epoxidation method not using epichlorohydrin is demanded. As the production method to meet this demand, a method of condensing an allyl alcohol by the use of a palladium catalyst to form an allyl ether and then obtaining an epoxy compound by the use of hydrogen peroxide or an organic peroxide has been advocated (see, for example, Patent Document 1). However, this method is not a practical method, because the palladium is very expensive and for preventing the residual palladium from contacting with an oxide such as peroxide to decompose the peroxide, a cumbersome process of purifying and removing the palladium is necessary.
A method of producing an allyloxy form with a low chlorine content and oxidizing the allyloxy form to effect conversion to an epoxy compound, thereby synthesizing a glycidyl ether having a low chlorine content, has been recently developed (see, for example, Patent Documents 2 and 3).
The epoxidation reaction employed in this production method is generally performed by allowing onium salts such as ammonium salt and at least either a tungsten compound or a molybdenum compound to exist together and using hydrogen peroxide as an oxidant (epoxidizing agent) (see, for example, Non-Patent Documents 1 to 3).
This epoxidation reaction generates only water as a byproduct and therefore, is a clean reaction producing less waste, compared with an epoxidation reaction using an organic peroxide typified by peracetic acid. In addition, since aqueous hydrogen peroxide of 30 to 45% is used, the procurement and handling are easy and simple.
However, in this epoxidation reaction, the oxidant is prepared using, as an onium salt usually allowed to coexist as a catalyst, an ammonium salt having a long-chain alkyl group, such as methyltrioctylammonium chloride, or a pyridinium salt having a long-chain alkyl group, such as cetylpyridinium salt. The onium salt having a long-chain alkyl group has a high distribution factor to an organic solvent and poses a problem that it is very difficult to, after the reaction, separate and purify the epoxy compound dissolved in the organic phase from the catalyst composition-derived components, specifically, tungsten, an onium salt, and an onium salt-derived nitrogen-containing compound. Furthermore, when tungsten, a nitrogen-containing compound and the like are removed by a method such as recrystallization and suspension-washing, there is a problem that the purification yield (recovery percentage) of the epoxy compound is low.
Therefore, catalyst-derived heavy metal components such as tungsten and molybdenum, or ionic compounds such as onium salt, remain in the obtained epoxy compound. These components or compounds remain also in an epoxy resin produced from the epoxy compound and adversely affect the product.
Specifically, it has been reported that in the case where a heavy metal such as tungsten remains in the epoxy compound, an epoxy resin produced using the epoxy compound develops significant coloration when left standing under high-temperature conditions (see, for example, Patent Document 4). Also, in the case of using the epoxy resin for an electronic material, a halogen such as chlorine remaining in the epoxy compound gives rise to corrosion of wiring, and the remaining metal or ionic compound such as onium salt gives rise to short circuit or corrosion of wiring.
As the method for solving this problem, several methods have been reported.
For example, in Patent Document 5 or 6, a method where, after the epoxidation ration, the ammonium salt is absorbed and removed by using, as an adsorbent, an ion-exchange resin, a metal oxide or the like, is studied.
Also, in Patent Documents 7 and 8 and Non-Patent Document 4, a method where the ammonium salt employed for the epoxidizing agent is used in the state of being supported on a resin, silica gel or the like and then separated/recovered by filtration, is studied.
In Patent Document 9, a method where an ammonium salt used as the catalyst is precipitated after the epoxidation reaction, is studied.
In addition, in Patent Document 10, a method of disproportionating the catalyst is studied.
Furthermore, in Patent Document 11, a method of removing an ammonium salt by binding a magnetic material thereto is studied.